Supercharged furnace



March 29, 1938.

R. ANXION'NAZ SUPERCHARGED FURNACE Filed Apiil 27, 1936 Pastas M... 2a, 1938 ITED STATES,

PATENT OFFICE 1 Claims. ((21. sac-) In the case of flreboxes supercharged by means of a blower driven by a turbine utilizing the energy'of gases of combustion, it is known that, for

a given supply of fuel, there is only one speed of the turbo-blower unit at which parity existsbetween the power applied to the blower and that received by the gas turbine. This speed corresponds with a certain delivery of air, and there- .fore with a certain weight of air per kilogramme of fuel. It is found that this latter proportion is not the same in the case of variations in the quantity of fuel supplied. However, in order to obtain optimum conditions of combustion, it is important that the proportion ofair and fuel should remain approximately constant under all running conditions. In the case of heavy oil, for example, the desired proportion is about 16 kg. of air per kilogramme of heavy oil.

In accordance with the foregoing, balance of power in the blower and turbine, in the case of this proportion of air, exists only for a givenrate of combustion corresponding to a given speed of rotatlonbf the turbo-blower.

' become excessive and equilibrium is established,

in the unit, for a speed corresponding" with an excess of air as compared with the proportion mentioned above.

- On the other hand, in the case of lower rates. the power supplied to the gas turbine decreases more rapidly than that necessaryfor compressing the air; so that, in order to;prevent a lack-of i an of combustion and to restore-tho optimum proportion, it is necesary to provide the unit with a supply of motive power from a prime mover of some kind, such as, by way of concrete example, a steam turbine. I

For a given supply of fuel, this supply of power will obviously be more extensive when" it is desired to eilect the combustion with a greater excess of air. It is therefore, conceivable that the control of the excess of air may be eifected solely by exerting influence on the said supply of power, for example on the admission of steam when the power is supplied by a steam turbine;

It should-be noted however, that, in general,-

I this power represents only a small fraction of the total power, so that the slight variations to which it will be subjected, have only a very gradual effeet on the running ofthe unit, the management of which will therefore be rendered dimcult.

Moreover, in the case of operative conditions beyondthe state oi. equilibrium, and in which, of

' tain, or even accentuate auxiliary motor, 3.

course, the said supply of'power will not be provided, this method of control islacklng and, in general, the excess of air tending to occur is reduced by acting on the gases admitted into the turbine, either by diverting a portion of said gases,

or by throttling the intake or exhaust of the turbine. Such arrangement leads to control members, the embodiment of which is a critical matter, by reason of the high temperature and large volume of the gases'to be controlled.

Finally, in the 'case of boiler fl reboxes, the following circumstance further increases the dimculty of control. when, starting with a controlled combustion, the excess of air is increased, whilst the fuel supply remains the same, a rise in the temperature of the gases at the delivery end of the sheaf of tubes is usually observed. This is due chiefly to the heat exchange being reduced out of proportion to the lowering of the tempera- .ture in the firebox. Consequently, if a slight disturbance of equilibrium should occur accidental- 'ly, corresponding to an increased delivery of air,

followed-by a rise inthe temperature of thegases, the gas turbine willbe supplied with more power. tend to increase in speed and therefore mainthe said disturbance of equilibrium. It is conceivable that, in certain cases, a phenomenon that is unstable, within certain limits at least, may occur.

According to the present invention the control of combustion is effected by a branch located, in the main air circuit, between the delivery of the blower and the, intake of the gas turbine, and provided with a throttle or adjustable damper. The control obtained in this manner is far more sensitive, and prevents the above-mentioned unstable eflect.

In the accompanying drawing which illustrates by way of example, an embodiment of the invention':

Figure 1 is a diagrammatic sectional elevation of a device adapted to the special case of a boiler firebox under pressure, and.

Figure 2 is a diagrammatic section of a gas turbine, showing an arrangement for cooling the rotor of said turbine.

As shown in Figure 1 a blower l is driven by a gas turbine 2, and by a steam turbine, or other Air drawn in through an intake I is delivered to the combustion chamber and liquid fuel is supplied to a burner 8 through a pipe 1. After having passed through a sheaf of tubes 8 in the boiler, the gases of combustion reach the gase turbine 2, by way of a conduit I, and leave it through a conduit ll.

The power of the auxiliary motor I is controlled, for each set of working conditions of the boiler, in such a manner that the blower delivers a slight excess of air, for example 10/ in relation to the amount that would be sufllcient to burn the fuel consumed under said conditions. It should be noted that it is. thus necessary to provide a larger supply of power than if the object v were to supply only the amount of air strictly needed for combustion, but, as a matter'of fact,

the compression of this excess air costs very little, since a large portion of the power thus expended is recovered in the gas turbine.

The air furnished by the blower l is divided into two portions, the one, passing into the air distributors of the burners, ensuring the combustion and, .after havingtraversed the boiler tubes 8-reaching the intake of the gas turbine 2, whilst the other, which passes direct to the intake of the turbine 2 by way of the branch H mingles with the gases of combustion. A throttle or damper l2 controls that portion of the delivery which passes into the branch II, in sucha man-' ner that the main portion, which passes into the firebox, corresponds with optimum combustion.

The throttle i2 may be acted upon by hand, or by means of an automatic device ensuring, for example, the maintenance of a constant ratio between the supplies of air and heavy oil. Many an existing proportional control devices may be employed for this purpose, the principle of one such being represented, by way of example, in Figure 1. l

Before reaching the burner 6' the liquid fuel passes through a Venturi device 13, in which it undergoes a pressure drop proportional to the square of the supply. The elastic diaphragm ll of a manometric capsule I5 is exposed to this differential pressure and another manometric capsule lB-also provided with an elastic diaphragm l|isexposed to the diflerential air pressure between the two points l8 and I, the one located at the entrance to the boiler, and the other at the outlet end of the tubes 8. This pres- 5 sure difference is proportional to the square of the air delivery. The two diaphragms are connected by a rod 20 and are so arranged that the efforts to which they are exposed act in opposition. It will be evident that the equilibration 0 corresponds with the proportional values of the difierential pressures, that is to Bay. of the supplies of air and fuel. The movements of the rod 20 are transmitted to the control throttle l2 through a train of levers articulated at 2|, 22, 23. 55 If the supply of fuel is increased, the depression in the venturi I3 also increases and. acting on the diaphragm ll. causes the throttle I! to close. The supply of air passing into the combustion chamber therefore increases at once. At the 0 same time, the temperature of the gases of combustion rises. The gas turbine, which thus receives more power, speeds up progressively and the blower delivers more air. The suction between the points II and I! increases and, acting as on the diaphragm l'l, tends to reopen-the throttle l2, until proportionality is restored between the new supplies of air and fuel. The conditions are reversed when the supply of fuel is reduced.

- This control functions in a similar manner inv 70 the case of running speeds higher than that at which theses turbine is able to drive the blower.

unaided. It is known that, for these conditions, thepower of the gases is more than suilicient, and

' the unit tends to furnish a considerable excess 75 of air by itself. The aperture of the throttle 12' adjusts itself in such a manner as always to off by way of the branch II and serving to cool the gases at the intake of the turbine, thereby tending to lessen the power received by the latter, and, consequently, to limit its speed.

In the case of conditions approximating to the maximum speed of the unit, it is evident that the blower, which delivers a considerable excess of air, is called upon to run at a higher speed. than would be necessary for supplying Just enough air to burn the maximum supply of fuel. This may ive rise to inconvenience if the rotor has been designed solely to stand the stresses corresponding with the maximum running conditions. In such a case it is necessary to be able to slow down the unit. All that is required for this contingency is the provision of a control member producinga pressure drop at any point in the air circuit, or the gas circuit, such as a throttle 10- ticulated at 28-21, to a throttle or damper 2| arranged in an air branch 28 provided on the delivery of the blower.

When the speed exceeds a given value, this throttle 28 opens. thus reducing the supply of gas passing to the turbine, and consequently reducing the power of the latter and automaticallylessening the speed. In the example shown in Figure 2, this air branch 2! is utilized for cooling the rotor of the gas turbine.

The air from the branch 20 is'distributed between the two branch pipes Ill and II opening' into the two chambers 32 and II of the gas turbine communicating with theexhaust. It then cools the two sides of the rotor ll, by circulating in the spaces 35 and I! provided between the rotor and stator of the turbine. This supply of fresh air increases with the speed, and therefore with the load on the boiler, a particularly advantageous circumstance in view ofthe fact that the gases are then at their highest temperature.

What I claim is: Y 1. A' system including a supercharged furnace which comprises, in combination, means for feeding-liquid fuel to said furnace, a blower arranged to feed air to said furnace, means, including a gas turbine, for driving said blower, means for feeding the combustion gases from said furnace as motive fluid to the intake of said gas turbine, adjustable means for feeding a variable portion of the air delivered by said, blower directly to the intake of said turbine, and means responsive to variations in the ratio of the rates of feed of said fuel and said air, respectively, to said furnace for controlling said adjustable means.

2. A systemincluding a supercharged furnace which comprises, in combination, means, including a conduit for feeding liquid fuel to said furnace, ablower arranged to feed air to said furnace, meima'including a gas turbine, for driving said blower, means for "feeding the combustion gases from said furnace as motive fluid to the intake of said gas turbine, a venturi inserted in series in said conduit, a passage connecting the outlet of said blower directly to the intake of said gas turbine, regulating means for controlling theflow of air through said passage,- and means, operative by the combined actions of the suction producedsby said venturi in said conduit and of the difference between the pressure of the air discharged from said blower and the pressure of the gases fed to said turbine, for controlling said regulating means.

3. A system including a supercharged furnace which comprises, in combination, means, including a conduit for feeding liquid fuel to said furnace, a blower arranged to feed air to said furnace, means, including a gas'turbine, for driving said blower, means for feeding the combustion gases from said furnace as motive fluid to the intake of said gas turbine, a venturi inserted in series in said conduit, a conduit connecting the outlet of said blower directly to the intake of saidgas turbine, regulating means for controlling the flow of air through said last mentioned conduit, a manometric capsule, a diaphragm in said capsule, meansfor connecting the portion of said capsule located on one side of said diaphragm with the part of said first mentioned conduit 10-,

cated before said venturi,means for connecting the portion of said capsulelocated on the other side of said diaphragm with said venturi, another manometric capsule, a diaphragm forming a partition in said second capsule, means for connecting the portion of said second capsule located on one side of said last mentioned diaphragm with the outlet of said blower, means for connecting the portion of said second mentioned capsule located on the other side of said last mentioned diaphragm with the intake of said,

turbine, and means, operative by both of said diaphragms, for controlling said regulating means.

,4. A system including, in combination, a supercharged furnace, means for feeding liquid fuel to said furnace, a blower arranged to feed air to said furnace, means, including a gas turbine, for

driving said blower, means for feeding the combustion gases from said furnace as motive fluid to the intake of said gas turbine, a conduit connecting the outlet of said blower directly to the intake of said turbine, regulating means for controlling the flow of air through said conduit,

means for causing ayariableportion of the air,

delivered by said blower to escape into the atmosphere, and a governor, operative by saidv blower, for operating the last mentioned means when the speed of rotation of the blower exceeds a given value.

5. A system including a supercharged furnace which comprises, in combination, means for 3 feeding a non-solid fuel to said furnace, a blower arranged to feed air to said furnace, means, including a gas turbine, for driving said blower,

means for feeding the combustion gases from said furnace as motive fluid to the intake of said gas turbine, adjustable means for feeding a variable portion of the air delivered by said blower directly to the intake of said turbine, and means, responsive to variations in the ratio of the rates of feed of said fuel and said air, respectively, to said furnace, for controlling said adjustable means.

6. A system includinga supercharged furnace which comprises, in combination, means for feeding liquid fuel to said furnace, a blower arranged to feed air to said furnace, means, including a gas turbine, for driving said blower, means for feeding the combustion gases from said furnace as motive fluid to the intake of said gas turbine, a conduit connecting the outlet of said blower directly to the intake of said turbine, regulating means for controlling the flow of air through said conduit, and means, responsive to variations in the ratio of the rates of feed of said fuel and said air, respectively, to said furnace, for controlling'said regulating means.

'1. A system including a supercharged furnace which comprises, in combination, means, including a conduit, for feeding liquid fuel to said furnace, ablower arranged to feed air to said furnace, means, including a gas turbine, for driving located on the other side of said diaphragm with said venturi, another manometric capsule, a diaphragm forming a partition in said second mentioned capsule, means for connecting the portion of said second mentioned capsule located on one side of said last mentioned diaphragmwith the outlet of said blower, means for connecting the portion of said second mentioned capsule located on the otherv side of said last mentioned diaphragm with the intake of said turbine, a rod intereonnecting said two diaphragms, and means operatively connected with said rod for controlling saidregulating means.

BIN! ANZIONNAZ. 

